1. Field of the Invention
The present invention relates generally to a solenoid valve for brake systems, and more particularly, to a solenoid valve for brake systems, which is designed to sequentially open or close its fluid passage in two stages, thus being easily opened or closed even under excessive braking pressure, as well as allowing the fluid passage to be widely opened.
2. Description of the Prior Art
Generally, an anti-lock brake system (ABS) for vehicles is installed at a position on the brake fluid line so as to interrupt and adjust braking pressure which is applied to the wheels. Such an ABS is provided with a plurality of solenoid valves for selectively opening the fluid line of the ABS in response to control signals.
Such a solenoid valve for ABSs, as shown in FIG. 1, is pressure-fitted into a valve fitting hole 14 of a modulator block 13, and has a hollow valve housing 1 which is provided with an inlet 3 and an outlet 4. Fluid flows from the inlet 3 to the outlet 4.
A cylindrical sleeve 6 is coupled to an end of the valve housing 1. An armature 5 is axially installed in the sleeve 6 such that it can axially move in opposite directions. A valve core 7 is fitted into the open end of the sleeve 6, thus closing the open end of the sleeve 6 as well as biasing the armature 5. In order to selectively open the orifice 8a of a valve seat portion 8 in response to an axial movement of the armature 5 in either direction, a plunger 5a extends into the valve seat portion 8 which is formed in the bore 2 of the valve housing 1. In this case, the plunger 5a is formed on the end of the armature 5 in such a way as to be integrated with the armature 5.
A restoring spring 9 is installed between the armature 5 and the valve core 7, and applies an elastic restoring force to the armature 5 such that the armature 5 normally keeps the orifice 8a closed. Further, an exciting coil 10 is installed at a position outside of both the sleeve 6 and the valve core 7 for activating the armature 5.
In this solenoid valve, when electric power is applied to the exciting coil 10, an electromagnetic force is generated between the valve core 7 and the armature 5. As the armature 5 moves toward the valve core 7 by the electromagnetic force, the orifice 8a of the valve seat portion 8 is opened. On the other hand, when electric power is not applied to the exciting coil 10, the electromagnetic force does not occur. At this time, the armature 5 is returned to its original position by the elastic force of the restoring spring 9, so the orifice 8a is closed.
However, such a conventional solenoid valve has a problem in that an excessively large electromagnetic force is required to open the orifice 8a by actuating the armature 5, because the initial actuation of the armature 5 is not smooth due to the pressure of the inlet 3, when the plunger 5a of the armature 5 closes the orifice 8a and the pressure of the inlet 3 is large.
Furthermore, in order to accomplish rapid rising in braking pressure by opening and closing the solenoid valves for brake systems, the cross-sectional area (opening ratio of the passage) of the orifice 8a has to be large in order to allow a large quantity of fluid to pass. However, the conventional solenoid valve has another problem that its opening and closing action has poor reliability, because an excessively large force is required to open the valve due to the increased pressure of the inlet 3, as the cross-sectional area of the orifice 8a becomes large. Thus, in an effort to solve the problem, there has been proposed another solenoid valve, which is designed to be easily opened and closed by applying a large force (electromagnetic force) to the armature 5. In this case, the solenoid valve has a further problem in that it generates much operating noise. In addition, said solenoid valve has still another problem in that the volume of the exciting coil 10 has to be large to generate a large magnetic force.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a solenoid valve for brake systems, which is sequentially opened or closed in two stages, thus being easily opened or closed with a weak force even when unexpected large braking pressure is applied to an inlet of the valve. In addition, the present invention provides a solenoid valve, which is designed to widely open its fluid passage, thus rapidly increasing the pressure of the fluid line of a brake system.
In order to accomplish the above object, the present invention provides a solenoid valve for brake systems having a hollow valve housing provided on its outer circumferential surface with a fluid inlet and provided on its lower end with a fluid outlet, and an armature provided with a plunger extending into a bore of the valve housing in such a way as to selectively open a fluid passage from the inlet to the outlet while moving by electric power, said solenoid valve comprising: a spool movably set in the valve housing, provided along its central axis with the first orifice having a predetermined diameter, and provided at a position around the plunger with a plunger guide having a predetermined depth for allowing the plunger to enter the spool and open or close the first orifice; a valve seat portion formed on the inner surface of the bore of the valve housing by stepping the surface, defining a second orifice therein and coming into contact with or spaced from the end of the spool to selectively open the outlet separately from the first orifice when the spool moves in either direction, the second orifice having an inner diameter larger than that of the first orifice; and a spool restoring spring biasing the spool toward the plunger.
According to the present invention, a stopping means is provided on each of the inner surface of the plunger guide and the outer surface of the plunger, and allows the plunger to move relative to the spool within a predetermined range. The stopping means of the plunger guide is caught by the stopping means of the plunger to allow the spool to be pulled by the plunger when the plunger moves beyond the predetermined range. Further, the stopping means includes a recess formed on the inner surface of the plunger guide, and having a predetermined width in an axial direction of the spool, and a locking projection protruding from the outer surface of the plunger so as to engage with the recess.
In this invention, a spring holding portion is formed on the outer surface of the spool at a position around the valve seat portion, defining a space for seating the spool restoring spring, and having an outer diameter smaller than an inner diameter of the bore of the valve housing for allowing fluid to flow from the inlet to the outlet when the spool is spaced from the valve seat portion.
According to this invention, at least one radial path is formed on the plunger guide of the spool such that the first orifice communicates with the inlet through the radial path.
Furthermore, in the present invention, a reinforcing member, made of a material having strength higher than that of the valve seat portion, is installed on the valve seat portion to prevent the valve seat portion from being deformed when the valve seat portion comes into contact with the spool.